Re: [PATCH v3 2/2] selftests: Add test for overriding global data value before load

On Sun, Mar 29, 2020 at 6:10 AM Toke Høiland-Jørgensen [off-list ref] wrote:

Andrii Nakryiko [off-list ref] writes:

quoted

On Sat, Mar 28, 2020 at 11:29 AM Toke Høiland-Jørgensen [off-list ref] wrote:

quoted

This extends the global_data test to also exercise the new
bpf_map__set_initial_value() function. The test simply overrides the global
data section with all zeroes, and checks that the new value makes it into
the kernel map on load.

Signed-off-by: Toke Høiland-Jørgensen <redacted>
---
 .../selftests/bpf/prog_tests/global_data.c    | 61 +++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/global_data.c b/tools/testing/selftests/bpf/prog_tests/global_data.c
index c680926fce73..f018ce53a8d1 100644
--- a/tools/testing/selftests/bpf/prog_tests/global_data.c
+++ b/tools/testing/selftests/bpf/prog_tests/global_data.c

@@ -121,6 +121,65 @@ static void test_global_data_rdonly(struct bpf_object *obj, __u32 duration)
              "err %d errno %d\n", err, errno);
 }

+static void test_global_data_set_rdonly(__u32 duration)
+{
+       const char *file = "./test_global_data.o";
+       int err = -ENOMEM, map_fd, zero = 0;
+       __u8 *buff = NULL, *newval = NULL;
+       struct bpf_program *prog;
+       struct bpf_object *obj;
+       struct bpf_map *map;
+       size_t sz;
+
+       obj = bpf_object__open_file(file, NULL);

Try using skeleton open and load .o file, it will cut this code almost
in half.

Doesn't work, though:

Right, because test_global_data uses BPF-only struct definitions. In
real life those types should be shared in a common header file.

For this feature, I'd suggest to create a separate trivial BPF program
with a simple trivial BPF program and single global variable. There is
nothing you really need from test_global_data setup.

In file included from /home/build/linux/tools/testing/selftests/bpf/prog_tests/global_data_init.c:3:
/home/build/linux/tools/testing/selftests/bpf/test_global_data.skel.h:31:14: error: field ‘struct1’ has incomplete type
   31 |   struct foo struct1;
      |              ^~~~~~~
/home/build/linux/tools/testing/selftests/bpf/test_global_data.skel.h:37:14: error: field ‘struct3’ has incomplete type
   37 |   struct foo struct3;
      |              ^~~~~~~
/home/build/linux/tools/testing/selftests/bpf/test_global_data.skel.h:45:14: error: field ‘struct0’ has incomplete type
   45 |   struct foo struct0;
      |              ^~~~~~~
/home/build/linux/tools/testing/selftests/bpf/test_global_data.skel.h:46:14: error: field ‘struct2’ has incomplete type
   46 |   struct foo struct2;
      |              ^~~~~~~
make: *** [Makefile:361: /home/build/linux/tools/testing/selftests/bpf/global_data_init.test.o] Error 1

Just fixing the program SEC name as you suggested below already gets rid
of half the setup code, though, so doesn't really make much difference
anyway :)

quoted

quoted

+       if (CHECK_FAIL(!obj))
+               return;
+       prog = bpf_program__next(NULL, obj);
+       if (CHECK_FAIL(!prog))
+               goto out;
+       err = bpf_program__set_sched_cls(prog);

Please fix SEC() name for that program instead of setting type explicitly.

Yeah, that helps, thanks!

quoted

quoted

+       if (CHECK_FAIL(err))
+               goto out;
+
+       map = bpf_object__find_map_by_name(obj, "test_glo.rodata");
+       if (CHECK_FAIL(!map || !bpf_map__is_internal(map)))
+               goto out;
+
+       sz = bpf_map__def(map)->value_size;
+       newval = malloc(sz);
+       if (CHECK_FAIL(!newval))
+               goto out;
+       memset(newval, 0, sz);
+
+       /* wrong size, should fail */
+       err = bpf_map__set_initial_value(map, newval, sz - 1);
+       if (CHECK(!err, "reject set initial value wrong size", "err %d\n", err))
+               goto out;
+
+       err = bpf_map__set_initial_value(map, newval, sz);
+       if (CHECK_FAIL(err))
+               goto out;
+
+       err = bpf_object__load(obj);
+       if (CHECK_FAIL(err))
+               goto out;
+
+       map_fd = bpf_map__fd(map);
+       if (CHECK_FAIL(map_fd < 0))
+               goto out;
+
+       buff = malloc(sz);
+       if (buff)
+               err = bpf_map_lookup_elem(map_fd, &zero, buff);
+       CHECK(!buff || err || memcmp(buff, newval, sz),
+             "compare .rodata map data override",
+             "err %d errno %d\n", err, errno);
+out:
+       free(buff);
+       free(newval);
+       bpf_object__close(obj);
+}
+
 void test_global_data(void)
 {
        const char *file = "./test_global_data.o";

@@ -144,4 +203,6 @@ void test_global_data(void)
        test_global_data_rdonly(obj, duration);

        bpf_object__close(obj);
+
+       test_global_data_set_rdonly(duration);

This should either be a sub-test or better yet a separate test
altogether.

Sure, will move it to its own file.

-Toke